1. Field of the Invention
The present invention generally relates to a hydraulic braking system for an automotive vehicle. More specifically, the present invention relates to a control device for controlling hydraulic brake fluid applied to respective wheel cylinders provided for each wheel of an automotive vehicle.
2. Description of the Prior Art
In a hydraulic braking system for an automotive vehicle, brake fluid is supplied to the brake cylinder provided for each wheel of the vehicle. When the foot pedal is moved from the released position to the braking position and thus fluid is supplied to the brake cylinders to apply the brake, it is possible for the rear wheels to lock the front wheels. This is very dangerous and can result in the vehicle skidding.
Practically, when the vehicle is driven and the braking system is temporarily applied, the inertia of the vehicle increases the load applied to the front axle and thus to causes the load to be distributed unevenly between front and rear wheel axles. Meanwhile, upon braking the vehicle, it will be apparent the wheels subject to a relatively light load will lock before the others. Thereby, if the same fluid pressure is applied to both front and rear wheels, it may cause the rear wheels to lock in advance of the front wheels and result in the vehicle skidding.
To prevent the vehicle from skidding, a control valve means has been provided in the hydraulic circuit connecting a master cylinder to the wheel cylinder for each rear wheel. This conventional control valve means controls the supply of brake fluid to the rear wheel cylinders to limit the value of the pressure applied to the rear wheel cylinder. Although this control valve means can prevent the vehicle from skidding because of a difference of brake application timing between the front and rear wheels, it cannot correct for an uneven load on the right and left sides. A difference in the load on the right and left side wheels may be caused, for example, by braking when the vehicle is going round a curve; then, clearly, the load applied to the other wheels is larger than that applied to the inner wheels. Then, if the braking system is operated to decelerate the vehicle, the different load on inner and outer wheels causes a lop-sided braking action.
Further, as the conventional control valve means is merely provided in the hydraulic circuit connecting the master cylinder with the rear wheel cylinders, it is impossible to adjust the ratio of pressure fluid supplied to the front wheel cylinders. If the load applied to the rear wheel or wheel axles is smaller than that applied to the front wheel cylinder, it will not be possible to control the ratio of fluid pressure.
Yet further, the conventional control valve means controls both rear wheels together and cannot compensate for loads applied to each rear wheel separately. Therefore, the above-mentioned control valve means cannot completely prevent the vehicle from skidding.
To prevent the vehicle from skidding completely, it will be necessary to alter the hydraulic pressure applied to each wheel corresponding to the relative of the load applied thereto.